The present invention relates to high-bypass gas turbine engines, and more particularly to thrust reverser systems utilized in high-bypass turbofan engines to provide thrust reversal by diverting air from a fan bypass duct.
FIG. 1 schematically represents a high-bypass turbofan engine 10 of a type known in the art. The engine 10 is schematically represented as including a nacelle 12 and a core engine (module) 14. A fan assembly 16 located in front of the core engine 14 includes a spinner nose 20 projecting forwardly from an array of fan blades 18. The core engine 14 is schematically represented as including a high-pressure compressor 22, a combustor 24, a high-pressure turbine 26 and a low-pressure turbine 28. A large portion of the air that enters the fan assembly 16 is bypassed to the rear of the engine 10 to generate additional engine thrust. The bypassed air passes through an annular-shaped bypass duct 30 between the nacelle 12 and an inner core cowl 36 that surrounds the core engine 14, and exits the duct 30 through a fan exit nozzle 32. The nacelle 12 defines the radially outward boundary of the bypass duct 30, and the core cowl 36 defines the radially inward boundary of the bypass duct 30 as well as provides an aft core cowl transition surface to a primary exhaust nozzle 38 that extends aftward from the core engine 14.
The nacelle 12 is typically composed of three primary elements that define the external boundaries of the nacelle 12: an inlet assembly 12A, a fan cowl 12B interfacing with an engine fan case that surrounds the fan blades 18, and a thrust reverser system 12C located aft of the fan cowl 12B. The thrust reverser system 12C comprises three primary components: a translating cowl (transcowl) 34A mounted to the nacelle 12, a cascade 34B mounted within the nacelle 12, and blocker doors 34C shown in a stowed position radially inward from the cascade 34B. The blocker doors 34C are adapted to be pivotally deployed from their stowed position to a deployed position, in which the aft end of each blocker door 34C is pivoted into engagement with the core cowl 36 as represented in phantom in the upper half of FIG. 1. In this sense, the core cowl 36 can also be considered as a component of the thrust reverser system 12C. The cascade 34B is a fixed structure of the nacelle 12, whereas the transcowl 34A is adapted to be translated aft to expose the cascade 34B and deploy the blocker doors 34C into the duct 30 using a link arm 34D, causing bypassed air within the duct 30 to be diverted through the exposed cascade 34B and thereby provide a thrust reversal effect. While two blocker doors 34C are shown in FIG. 1, a plurality of blocker doors 34C are typically circumferentially spaced around the circumference of the nacelle 12.
In a conventional thrust reverser design used in the high bypass turbofan engine 10, the cascade 34B is covered by the stowed blocker doors 34C when the thrust reverser system 12C is not in use, that is, during normal in-flight operation of the engine 10. A drawback of this type of conventional construction is that the transcowl 34A must have a sufficient length and thickness to accommodate the stationary cascades 34B, which results in compromises to the overall diameter of the nacelle 12 or the fan duct area, leading to higher Mach numbers and fan duct losses. In addition, because the blocker doors 34C define portions of the fan duct outer flow surfaces, surface interruptions (gaps and steps) and duct leakage resulting from the doors 34C can increase aerodynamic drag and reduce aerodynamic performance. In addition, the blocker doors 34C incorporate only limited areas of acoustic treatment as well as create discontinuities in the translating cowl acoustic treatment, and are exposed to damage and wear-inducing conditions during normal engine operation. These aspects of conventional thrust reversers can significantly reduce engine performance, engine noise attenuation, specific fuel consumption, and operational reliability.